206 Mr. O. Thomas on small Mammals 
these specimens therefore, whatever other co-types were 
mixed up with them, being able to be taken as lectotypes of 
their respective names. 
Now over most of the area concerned we seem to have two 
quite distinct forms of Akodon—A, with a short, normal- 
shaped, rather bowed skull, on whose m! a very distinct and 
fairly persistent anterior median notch is present, an animal 
externally lined greyish brown, with a contrasted white chin- 
spot, and B, with a flattened long-nosed skull, the m’ practi- 
cally without a notch, this only being perceptible in an 
aborted form in specimens with quite unworn teeth. Hxter- 
nally this animal is greyish or yellowish, with the feet more 
distinctly yellow, and the chin-spot not contrasted. 
Returning to the type-specimens, it is quite clear, as shown 
by their skulls and teeth, that both 55. 12. 24. 156 and 157. 
belong to B, and that therefore A is without aname. Young 
and supplementary specimens obtained by Darwin on the 
Rio Negro and at Port Desire are referable to A, but these 
do not affect the determinations, and I propose to give to the 
latter form the name of A. iniseatae. A local form of it, 
obtained by Sr. Budin, I now describe. ] 
11. Akodon iniscatus collinus, subsp. n. 
S$. 205, 208, 209, 210; 9. 206, 207, 218." Maiten, 
W. Chubut. 700 m. 
A more blackish race of A. ¢niscatus. A full description 
is given here instead of to the typical inzscatus, as quite fresh 
specimens are available of it, while those of that animal are 
less perfect. 
Size small, about as in wxanthorhinus and canescens, the 
tail short as in those southern species, not as in the arenicola 
group. General colour above dark grizzled olivaceous brown 
(more greyish olivaceous and less brown than Ridgway’s 
“ olive-brown’’), the hairs ticked with black and dull buffy ; 
sides rather more buffy. Under surface soiled greyish buffy, 
the hairs dark slaty at base, their ends drabby or buffy—a 
patch in the inguinal region more definitely buffy. Chin, or 
rather interramia, with a conspicuous patch of wholly white 
hairs, contrasting markedly with the general dark colour. 
Bars. short, their proectote blackish, their metentote buffy. 
Hands and feet brownish white. Tail short, well haired, 
strongly bicolor, black along the top, whitish or ’ puffy whitish 
on sides and below. 
Skull rather bowed above, its surface smooth and unridged. 
Interorbital edges square, not ridged. Palatal foramina long, 
